So as promised, here's the new design. It provides better readings ! I guess that I should involve a cube ball to be perfect :)
Anyway, its good enough, thx for the feedback... I'll try now to finalise the complete board and the ball launcher located at the bottom when the ball evades the flipper
For the programming part, I'm still using the "ugly" editor... And a very simple ball detection algo, maybe this can be improved as well :)